Here I have installed a caravan toilet ventilation system to my Thretford C260, which provides a comparable result as a commercially available kit from a German company (SOG). The Thretford C260 appears to have been designed to have an active venting system in mind as you will see in the video.

This makes this DIY project really quite simple and a very low cost addition to your van. This modification reduces or negates the need to add any chemicals to the cassette therefore lower cost to maintain, greater flexibility to dump as no chemicals makes it compatible with septic sewerage systems and reduces any odour in the van as the fan is always active while the toilet is in use.

The principal in use here can be adapted to other systems that have a passive vent pipe to the outside of the van (which most do as a necessity to vent any build up of gas in the cassette).

NOTE: I recently upgraded the fan to a Sunon 60mm fan to provide greater air throughput. The 50mm was OK just replacing the fan a a matter of course every couple of years and changed to the slightly bigger version.